Everyone knows that adding lemon juice to sliced fruit will keep it from browning, but it can also impart a bitter flavor to the fruit unless you balance it with a little sugar or other sweetener. Bento weblog Lunch in a Box recommends having a small container of water with lemon juice and sweetener ready to go in your fridge so you can quickly assemble lunches and snacks on the fly.

Lunch in a Box also notes that

any form of ascorbic acid (Vitamin C) will work including lime juice, orange juice, cream of tartar, a crushed vitamin C tablet dissolved in water, or even ground chili pepper. I like the flavor that orange juice adds to fruit, but often use bottled lemon juice with a little Splenda or sugar for the same effect without the pucker. Salt water also slows browning and adds an interesting savory bite to fruit.